In general, frames for supporting a glass sheet in a horizontal position are known, and currently used in various processes in the production of a glazing for a motor vehicle. In one known embodiment, the frame is formed by metal flats placed edgewise to provide bearing surfaces for the glass sheet. The bearing surfaces are provided with grooves forming evacuation channels. According to another embodiment, the frame is formed by flats placed horizontally. According to this embodiment, the flat surfaces of the flats substantially correspond to the shape of the glass sheet to be supported. The support instrumentality comprises a plurality of pins in horizontal position which support the glass sheet. The horizontal pins are provided on the inwardly directed edge of the flats.
The evacuation channels, between the edge of the glass sheet and frame, should be of sufficient section to assure a perfect tempering of the glass sheet even within the region of its edges. On the other hand, the distance between bearing surfaces should not be too great, because the placing of the glass sheet on different points with a too great distance leads to a optically disturbing deformation of the marginal zones of the glass sheet which is heated to its deformation temperature.
It has been found that the known frames cannot satisfy the two important requirements of perfect tempering within the marginal zones while, at the same time, and within those zones, avoiding substantially all optically disturbing deformation that may occur. In an attempt to satisfy these requirements, frames for use in the process of tempering of glass sheets oftentimes are covered with a fine mesh metal netting. The purpose of the netting is to multiply and equalize the points of contact of the glass sheet on the frame. It is also thought that the netting would provide a favorable influence for evacuation of the blowing air. It has been found, however, that the frame with a mesh leads to certain drawbacks. One particular drawback is that the mesh unfavorably influences the optical quality of the marginal zones of the glazing because the mesh has the very definite tendency to warp during in the tempering process.